Provided are ligand compounds selected from among N-(diphenylphosphino)-1,1-diphenyl-N-(4-phenylbutan-2-yl)phosphinamine and N.sup.4,N.sup.4-bis(diphenylphosphino)-N.sup.1,N.sup.1-diethylpentane-1,4-diamine, a catalyst system for olefin oligomerization, and a method for olefin oligomerization using the same. The catalyst system for olefin oligomerization has excellent catalytic activity, and yet, exhibits high selectivity to 1-hexene or 1-octene, thus enabling more efficient preparation of alpha-olefin.

A method for preparing cis-1,4-polydienes, the method comprising the steps of preparing a preformed, active lanthanide-based catalyst, aging the active lanthanide-based catalyst for more than 5 days to thereby formed an aged catalyst, and introducing the aged catalyst and conjugated diene monomer to be polymerized to thereby form an active polymerization mixture in which the conjugated diene monomer is polymerized to form a polydiene having a reactive chain end.

A method for preparing cis-1,4-polydienes, the method comprising the steps of preparing a preformed, active lanthanide-based catalyst, aging the active lanthanide-based catalyst for more than 5 days to thereby formed an aged catalyst, and introducing the aged catalyst and conjugated diene monomer to be polymerized to thereby form an active polymerization mixture in which the conjugated diene monomer is polymerized to form a polydiene having a reactive chain end.